Saw it , discarded it as part of the problem!
One of the difficulties is that several fungal issues can appear the same. For example it could be leaf spot that starts with reddish spots that develop a yellow centre. Rust spores are more evident on the surface normally, particularly on the twigs and fruit. The products you have used typically attack a broad spectrum of fungal issues so I would tend to be patient at this point. I had a similar but more extensive issue with princess persimmon in the early spring last year! Within three weeks infuse granules had it under control. I simply removed the badly affected leaves and watered the soil without wetting the foliage. The other step I would consider in the future is adapting soil mix to ensure better drainage and unsaturated growing condition for quince as they are very susceptible to fungal issues. For my Chojubai and Toyo Nishiki improved, as well as persimmon I have switched to lower amounts of Akadama, increasing pumice and lava to create a bit drier mix. I also ensure they are in a bit deeper containers to foster better root growth and more stable moisture levels!